Fresnel zone

About: Fresnel zone is a research topic. Over the lifetime, 2337 publications have been published within this topic receiving 37650 citations.

Signal detection by correlation of Fresnel diffraction patterns

Abstract: A typical problem of signal detection is the search for key words. This can be done automatically by means of optical matched filtering. Here we describe an alternative method in which the key word is used directly, not in the form of a matched filter. We compute optically the correlation integral of the intensity distributions of the Fresnel diffraction patterns from the input (printed page) and from the reference signal (key word). In the output plane a detection peak (light point) indicates the position of the key word on the input page.

Panel-mounted photovoltaic system with fresnel reflector

Abstract: A system comprises first and second Fresnel reflectors. Each of the Fresnel reflectors comprises a Fresnel surface with a focus, a radiating surface opposite the Fresnel surface, and a photovoltaic element mounted to the Fresnel surface, in thermally conducting contact with the radiating surface. The first and second Fresnel reflectors form a vertex having a dihedral angle, such that the focus of the first Fresnel reflector is directed toward the photovoltaic element on the second Fresnel reflector, and such that the focus of the second Fresnel reflector is directed toward the photovoltaic element on the first Fresnel reflector.

A New GIS-Based Algorithm to Support Initial Transmitter Layout Design in Open-Pit Mines

Abstract: In this paper, a new geographic information systems (GIS)-based algorithm is proposed for supporting the initial design of a wireless communications system in open-pit mines. In this algorithm, multiple candidate transmitter (wireless access point) locations are selected considering the probability of further development and environmental factors in the mine. Then, a three-dimensional (3D) partial Fresnel zone between the transmitter and the receiver is defined and its 3D Fresnel index calculated by communication viewshed analysis of topographic data. The initial design for a transmitter layout is then determined based on the 3D Fresnel indices, which are calculated for all candidate transmitter locations. The proposed algorithm was applied to an open-pit mine located in Samcheok-si, Gangwon-do, South Korea. The 3D Fresnel indices were calculated for 15 candidate transmitter locations, and an initial transmitter layout then designed considering favorable combinations of two, three, and four transmitters. The proposed algorithm provided more precise Fresnel index overlay maps for the favorable transmitter candidate combinations than other algorithms based on line-of-sight and two-dimensional partial Fresnel zone analyses. Application of the algorithm to an open-pit mine where a wireless communications system is already installed revealed that the initial transmitter layout design is acceptable in terms of providing reasonable information on the coverage area of transmitters. Because the proposed algorithm provides an initial transmitter layout that can be modified after field investigations, it can support efficient design of wireless communications systems for use in open-pit mines.

Radar Tomography For Cavities Detection

Abstract: Preliminary tests on laboratory models have enabled us to provide some guidelines for traveltime ray tomography with GPR applied to civil engineering problems, specifically to find voids in pillars, walls and structures. The width of the Fresnel zone and the source and receiver locations are the limits to resolution capability. For crosshole geometry a criterion to know resolution capability, based on detectable wavenumbers, is analytically derived. Acquisition and reconstruction parameters (source and receiver location, operating frequency, measurement number, acquisition time, slowness grid) are discussed and optimized with tomographic experiments on some models drilled expressly to produce voids. Tomography is solved by SVD, experimenting both regular and irregular gridding. An iterative procedure for noise reduction is proposed to improve the solution. A sort of black and white tomography is also applied to explore the actual limits of straight ray approximation. For crosshole geometry a wavenumber decomposition of the problem is proposed and the benefits discussed.